Conventionally, magnetic force microscope (MFM) is known as a device for observing magnetic fields originating from specimens.
One type of MFM is for observing alternating-current magnetic fields (AC magnetic fields) and the other type of MFM is for observing DC magnetic fields.
Since the present invention is an art related to MFMs for observing DC magnetic fields, hereinafter conventional MFMs for observing DC magnetic fields will be described.
FIG. 6(A) is a view to explain a conventional MFM for observing DC magnetic fields (see Patent Literature 1). In the MFM depicted in FIG. 6(A), a probe 811 of a cantilever 81 is made of a hard magnetic material. Once a hard magnetic material is magnetized, magnetization reversal thereof is difficult to occur. In FIG. 6(A), an alloy of cobalt and chrome, a compound of iron and platinum, or the like is employed as the hard magnetic material.
In the MFM of FIG. 6(A), the cantilever 81 is oscillated by a piezoelectric element 812 at a resonant frequency or a frequency close to the resonant frequency (for example, approximately 300 kHz). An alternating-current power supply for the oscillation is denoted by AC in FIG. 6(A). A magnetic interaction occurs between the probe 811 and a specimen 82.
This magnetic interaction causes apparent change in the spring constant of the cantilever 81. This apparent change in the spring constant makes the resonant frequency of the cantilever 81 change. As a result, a vibrating state (amplitude and phase) of the probe 811 also changes.
In the MFM of FIG. 6(A), the change of the amplitude and phase in the vibration of the probe 811 (change in the spring constant of the cantilever 81) is optically detected. This makes it possible to obtain distribution of a magnetic field gradient on the surface of the specimen 82 as an image.